1. Field of the Invention
The present invention relates to a method of spraying a strippable liquid paint on the surface of a large-sized product finished with a sprayed coating, such as an automobile, to form a protective film. Also, the invention relates to a machine for implementing this method and to a method of forming this protective film in such a way that those portions of the product which need no protective film are not sprayed with the paint.
2. Description of the Related Art
Typically after an automobile is assembled, it is initially kept in stock before it shipped. Therefore, a long interval passes until the vehicle is shipped. For this reason, dust or the like adheres to the surface of the sprayed coating on the outside of the automobile. In order to prevent this adhesion of dust, it has been attempted to form a protective film on the surface of the sprayed coating of the automobile. In the past, this formation of the protective film has been carried out by applying a liquid, rust preventive wax to the automobile's surface, which would be removed when the automobile reached its shipping destination.
In recent years, techniques for alleviating the burden imposed by a wax-removing operation performed at the destination or for environmental protection has been disclosed, for example in Japanese Patent Laid-Open No. 267171/1991. In particular, a plastic film having a removable pressure-sensitive adhesive is pressed against the surface of an assembled automobile finished with a sprayed coating, using a vacuum. Thus, the body surface is coated with this plastic film. In this way, the coating surface of the finished automobile is temporarily protected.
With respect to small parts, a strippable paint has been sprayed on them to form a protective film.
In the above-described known method consisting of coating the body surface with a plastic film, the whole surface of the automobile is covered with the protective film. Therefore, the protective film is stuck even on those portions which are not required to be protected such as the windshield. This leads to a cost increase.
Where a strippable paint is employed, it is possible to protect only desired portions. However, if the sprayed object is large such as an automobile, the protective film lacks uniformity because of nonuniform drying, the film is damaged by matter adhering to the surface of the coating, or other problems take place.
Where a strippable paint is applied to the surface of the coating of a finished automobile in an attempt to form a protective film for the coating, dust or the like often adheres to the surface of the coating. Also, dirty water may adhere to the surface. Furthermore, it may be wetted with rainwater or the like. In these situations, appropriate and smooth formation of the protective film is hindered when a strippable paint is applied. Moreover, the temperature of the surface of the coating drops. This makes it difficult to form a protective film on the surface of the coating.
Where a strippable paint is applied, the fringes of a region to be applied with the paint are applied with the paint, using a brush or a roller. Then, the paint is sprayed against the inner applied region surrounded by the fringes. In this way, a masking operation is dispensed with.
However, in some cases, components which are not required to be sprayed with paint such as windshield washer nozzles are located around the center of the region to which a strippable paint is applied. The washer nozzles are holes for ejecting cleaning liquid toward the windshield. In these cases, if the paint is sprayed against the hood after the paint has been applied to the fringes of the washer nozzles with a brush or nozzle, it is considerably difficult to perform the spraying operation in such a way that the paint does not adhere to the washer nozzles. Moreover, the strippable paint may be directly applied to the entrances to the windshield washer nozzles or enter the nozzles. Furthermore, dust of the paint may enter the nozzles. As a result, a film of the paint is formed at the entrances to the nozzles or even inside the nozzles. Hence, extra steps must be carried out to remove the film.
Where the roof of an automotive body may be opened such as a sliding roof, a conceivable paint application method consists of first applying the paint to the vicinities of the opening in the roof and to the vicinities of the engaging portion of the roof with a brush or roller and then spraying the paint against the remaining desired portions. However, a sealing member made of rubber is mounted around the opening in the roof and acts as a seal when the sliding roof is in a closed state. Therefore, there is the possibility that dust of the strippable paint enters the gap between the rubber seal and the sliding roof.
Side turning lights which are mounted to right and left fenders, respectively, on an automotive body via rubber seals have similar drawbacks. Therefore, a procedure for removing the protective film of a strippable paint is inevitable once the automobile reaches the destination. This procedure involves numerous steps.